1. Field of the Invention
The present invention relates to a communication network system for digital data distribution including terminal stations or work stations connected to one another by means of digital data transmission lines, and more particularly to a data-base managing architecture for automatically distributing an accessing load among the work stations by use of a distributed data-base management device for data distribution provided in each of the stations.
2. Description of the Related Art
Recently, a distributed data communication network system has received much more attention in place of a centralized data communication network system. In the centralized data communication network system, a host computer is used to control/manage data communication between work stations associated therewith. In contrast, in the distributed data communication network system, a distributed data-base management device is provided in each of the work stations, which controls data communication between the terminal station containing this management device and a terminal station or stations associated therewith. Therefore, each terminal may effect mutual data communication with a desired destination terminal independently of the other terminals.
A data-base network system can be given as one example of systems which most positively adopt the concept of data communication network. In this case, an internal data-base unit is provided in each of local work stations subscribed to the data-base system. The data-base unit can be freely accessed by not only the station (self station) containing the data-base unit but also any one of the remaining stations (external stations). In this sense, it is safe to say that information of the data-base unit of each station can be shared as the common information source by all the stations subscribed to the system.
In the conventional distributed data communication network system, however, it is extremely difficult to effectively perform the mutual access to data-base at a high response speed. One of the important reasons is that the data-base accessing load between the stations is not uniform. More specifically, when accessing requests of a number exceeding the load permissible level for the data-base of a certain work station are supplied from the other stations to the data-base of the certain work station, for example, it becomes impossible to effect rapid data communication therebetween. Particularly, in the conventional system, only one measure can be taken to cope with the above difficulty, and in this case, the operator uses a predetermined software command of an operating system to transfer at least part of data-base information of the certain station to another station whose load is now relatively small, thus distributing the data-base load. With such a manual load distribution management, it is almost impossible to fully cope with the continual change of the accessing load of the data communication.